Both insulin resistance and beta-cell dysfunction contribute to the pathogenesis of non-insulin dependent diabetes mellitus but controversy exists regarding which lesion is primary. In this study insulin resistance will be induced by administration of nicotinic acid (2 g orally daily for 4 weeks) in 15 lean (body mass index <25 kg/m2) Caucasian males with no family history of non-insulin dependent diabetes. The changes in glucose tolerance and beta-cell function will be studied.